Elongated wedge clamp assemblies are currently used for fastening a printed board assembly (PBA) or a PBA module to a channel of a rack or chassis. The wedge clamp assembly typically includes a plurality of wedges, each wedge having one or two ends with sloped surfaces. The sloped surfaces of each wedge abut against the sloped surface of the adjacent wedge. A screw extends length-wise through each wedge and connects together the plurality of wedges. The end wedge remote from the head of the screw typically has a threaded bore engaged by the screw such that a clockwise rotation of the screw draws the wedges toward each other, causing the wedges to deflect transversely from each other on the sloped abutting surfaces. This axial to transverse motion increases the assembly's width as its length is compressed, and thereby presses one side of the PBA or PBA module against the chassis channel wall, fastening the PBA or PBA module tightly within the chassis channel. Subsequently rotating the screw in a counterclockwise direction moves the wedges apart from each other, to bring them back into longitudinal alignment with each other and, thereby, to release the clamping force on the PBA or PBA module.
The expansion pressure of the wedge clamp is intended to mechanically lock the PBA or PBA module in position via static friction and to provide a low thermal resistance between the PBA or PBA module side and chassis channel wall that are in direct contact, as later described and shown in FIG. 1. The thermal resistance across a thermal interface is a function of the interfacing materials, the surface roughness, the contact area, and the contact pressure. The thermal resistance from the other PBA or PBA module side through the expanded wedge clamp and to the other chassis channel wall is much higher. This is due to the relatively small contact areas at the abutted hollow sloped wedge interfaces. These small contact areas create points of high thermal resistance, often referred to as thermal bottlenecks.
Some thermal bridge PBA modules are used, wherein thermal bridge structures are located on either side of the PBA such that the PBA is sandwiched between them, later described and shown in FIG. 2. Each thermal bridge structure has an external skin that is displaced from the printed board (PB) surface as needed to provide component clearance. Rib or post extensions from the thermal bridge external skin to the PB surface, typically at the PB periphery and periodically in between, provide PB mechanical support and PB heat sinking. Extensions from the thermal bridge external skin to the top of components provide component heat sinking. At the chassis channel interface, the thermal bridge external skin is not displaced from the PB surface and is in direct contact with the PB surface on either side to keep this interface narrow. A wedge clamp is mounted on one side of this interface to provide pressure to mechanically lock the thermal bridge PBA module in position. In this configuration, one thermal bridge is in direct contact with a chassis channel wall on one side and with one PB side on the other. The other thermal bridge is in direct contact with the other PB side on one side and with one wedge clamp side on the other side. The other wedge clamp side is in direct contact with the other chassis channel wall. In this configuration, because only one thermal bridge is in direct contact with a chassis channel wall, the thermal bridge on one side typically has a much lower thermal resistance to the chassis than the thermal bridge on the opposite side. Components on one side of the PBA module will therefore have a much higher thermal resistance to the chassis than components on the other side.